1. Field of the Invention
The invention relates generally to touchframe technology and, more particularly, to systems and methods for detecting a touch event within a touchframe perimeter.
2. Description of the Related Art
The operation of a typical scanning infrared (IR) touchframe system is based on the creation of a grid of invisible IR light beams above the viewing surface of a CRT monitor or flat panel display and the recognition of the location at which individual beams within the grid are interrupted. As shown in FIG. 1, to create such a grid, rows of IR light emitting diodes (LEDs) are paired with opposed rows of phototransistors of IR receivers. Each pair of LEDs and IR receivers constitutes an opto-pair or physical beam. The plurality of pairs create a horizontal (x-axis) and a vertical (y-axis) array of beams. The two arrays of beams and their circuitry make up an opto-matrix touchframe. An IR controller associated with the touchframe sequentially pulses the LEDs to create a grid of IR light beams (depicted as arrow lines). When a stylus, such as a finger, enters the grid, it obstructs the beams thereby resulting in a touch event. One or more of the IR receivers detect the absence of light and transmit signals that identify the X and Y coordinates of the touch event.
As shown in FIG. 2, a touchframe system designed to function with a flat panel is composed of an opto-matrix touchframe, an IR-transparent protective bezel and a transparent filter. To complete the touchframe system, the touchframe is linked to a modular touch controller (not shown) via a modular digital interface (MDI), which is a standard 8-pin telephone-type plug attached to the touchframe by an 8-pin cable.
Since IR touchframe systems operate using the IR portion of light, ambient light in the touch environment, i.e., the area surrounding the touchframe system, has long been a source of concern. Ambient light has varying levels of IR radiation, depending on whether the source of visible light is IR rich, as is sunlight, or IR poor, as is fluorescent light commonly used in offices. Ambient light and other optical noise in the touch environment may cause the touchframe system to provide false readings. For example, noise may cause an IR receiver to provide an output indicative of an unobstructed or connected light beam when the light beam is in fact obstructed or blocked. Conversely, in the presence of noise the IR receiver may provide an output indicative of a blocked light beam when the light beam is in fact connected.
As previously mentioned, the touchframe system sequentially pulses the LEDs to create a grid of IR light beams. A problem with such operation is that infrared light emitted by the sequential, regular pulsing of LEDs may leak into the surrounding environment and inadvertently activate devices which are remotely controllable using infrared remote controls. This can be a significant problem if the touchframe is on a medical devices, such as a ventilator, and it inadvertently activate other medical devices nearby.
Those skilled in the art have recognized a need for a touchframe system that is immune to noise in the touch environment. The need for a touchframe system that does not output interfering IR signals has also been recognized. The invention fulfills these needs and others.